1. Field of the Invention
The present invention relates to an image pickup (photographic) apparatus such as a video camera and, more particularly, to an image pickup apparatus in which a lens unit is interchangeable with respect to a camera main-body unit.
2. Related Background Art
A conventional video camera arranged as a camera built-in VTR cannot generally interchange lenses. As in a still camera using a silver chloride film, it is not easy to perform telephoto or wide-angled photography, thus narrowing a photographic range. A camera built-in VTR having interchangeable lenses is recently available on the market. However, this VTR does not have an auto-focus (AF) function and an auto-iris (auto-exposure or AE) function.
The present inventors have made extensive studies on developing a lens-interchangeable video camera having a lens unit which incorporates a photographic lens and an iris and which is detachable and interchangeable with respect to a camera main-body unit incorporating an image pickup element. In this video camera, a control unit including a microcomputer is arranged in the camera main-body unit and a lens unit. When the camera main-body unit is connected to the lens unit, the control units therein are connected through a data transmission line (communication line). In the camera main-body unit, a field brightness value from an image pickup element is detected, and an exposure operation is performed by the control unit in the camera main-body unit on the basis of the detected field brightness value. This exposure operation result is transmitted to the control unit in the lens unit. The control unit in the lens unit determines an iris opening amount on the basis of the exposure operation result and drives an iris driving means in accordance with the determined opening amount. The band of the field brightness signal in the camera main-body unit is limited by a plurality of band-pass filters. A focus operation of the control unit in the camera main-body unit is performed on the basis of the band-limited signal, and the operation result is transmitted to the control unit in the lens unit. The direction and speed of a focus motor are determined on the basis of the focus operation result in the control unit in the lens unit. A focus driving means is driven in accordance with the determined direction and speed.
In the lens-interchangeable image pickup apparatus having the exposure control system and the focus control system described above, when a user or photographer keeps disconnecting the lens unit from the camera main-body unit while the power switch of the lens unit is kept on, wasteful power is consumed, and a photographic time is undesirably shortened. Since electrical contacts of the mounting unit are exposed to the outer air, when the electrical contacts are short-circuited, the camera main-body unit is undesirably damaged.
In the lens-interchangeable video camera, picture recording is performed while the lens is properly mounted. If the lens is detached from the main-body or incomplete electrical connections occur between the lens and the camera main-body, the lens is set in an uncontrollable state. At this time, when the user erroneously touches a pushbutton type picture recording switch, an unnecessary picture is recorded although an optimal photographic operation cannot be performed. In this case, in order to erase the unnecessary recorded portion, a predetermined operation such as rewinding must be performed.
In the lens-interchangeable video camera, when the picture recording switch is touched in a lens uncontrollable state, picture recording is performed in a state except for the optimal photographic state, a cumbersome operation such as erasure of the unnecessary recorded portion must be undesirably performed.